U.S. patent number 7,314,496 [Application Number 10/493,056] was granted by the patent office on 2008-01-01 for honeycomb structure.
This patent grant is currently assigned to Ibiden Co., Ltd.. Invention is credited to Sungtae Hong, Teruo Komori, Kazushige Ohno.
United States Patent |
7,314,496 |
Hong , et al. |
January 1, 2008 |
Honeycomb structure
Abstract
A honeycomb structural body which is capable of increasing the
limiting collection amount of particulate, reducing the pressure
loss in use, and reducing fluctuations in the pressure loss even if
the flow rate from an internal combustion engine of exhaust gases
fluctuates. The honeycomb structural body is a columnar honeycomb
structural body in which a large number of through holes are
arranged side by side in the length direction with a partition wall
interposed therebetween. The large number of through holes are
constituted by a group of large-capacity through holes, with one
end thereof sealed to make the total cross-sectional areas
perpendicular to the length direction relatively greater, and a
group of small-capacity through holes, with the other end thereof
sealed to make the total cross-sectional areas relatively smaller.
The honeycomb structural body includes a plurality of columnar
porous ceramic members.
Inventors: |
Hong; Sungtae (Gifu,
JP), Komori; Teruo (Gifu, JP), Ohno;
Kazushige (Gifu, JP) |
Assignee: |
Ibiden Co., Ltd. (Ogaki-shi,
JP)
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Family
ID: |
31996168 |
Appl.
No.: |
10/493,056 |
Filed: |
September 16, 2003 |
PCT
Filed: |
September 16, 2003 |
PCT No.: |
PCT/JP03/11769 |
371(c)(1),(2),(4) Date: |
August 17, 2004 |
PCT
Pub. No.: |
WO2004/024293 |
PCT
Pub. Date: |
March 25, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050011174 A1 |
Jan 20, 2005 |
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Foreign Application Priority Data
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Sep 13, 2002 [JP] |
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2002-267819 |
Mar 4, 2003 [JP] |
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2003-057631 |
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Current U.S.
Class: |
55/523;
55/DIG.10; 55/484; 55/385.3; 55/282.3; 55/DIG.30; 60/311;
55/282.2 |
Current CPC
Class: |
B01D
46/4263 (20130101); B01D 46/0063 (20130101); F01N
3/027 (20130101); B01D 46/247 (20130101); F01N
3/0222 (20130101); F01N 3/023 (20130101); B01D
46/2425 (20130101); Y10S 55/30 (20130101); B01D
46/2488 (20210801); B01D 46/2451 (20130101); F01N
2330/06 (20130101); F01N 2330/34 (20130101); B01D
46/2459 (20130101); B01D 46/2474 (20130101); F01N
2450/28 (20130101); Y10S 55/10 (20130101); F01N
2330/30 (20130101); B01D 46/2498 (20210801); B01D
46/249 (20210801); F01N 2330/48 (20130101); B01D
46/2494 (20210801); F01N 3/2828 (20130101) |
Current International
Class: |
B01D
46/00 (20060101); F01N 3/023 (20060101) |
Field of
Search: |
;55/282.2,282.3,385.3,523,DIG.16,DIG.30,482,484 ;60/311
;428/116,117,118 |
References Cited
[Referenced By]
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JP |
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JP |
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JP |
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Apr 2001 |
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WO |
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WO 01/53232 |
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Jul 2001 |
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WO |
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02/10562 |
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WO |
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02/100514 |
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WO |
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WO 03/014539 |
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WO |
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03/020407 |
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WO |
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WO 03/044338 |
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May 2003 |
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WO |
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03/080218 |
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Oct 2003 |
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WO |
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Primary Examiner: Greene; Jason M.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
The invention claimed is:
1. A honeycomb structural body comprising: a plurality of porous
ceramic members combined with one another, the porous ceramic
members each having a plurality of large-capacity through holes and
a plurality of small-capacity through holes extending in parallel
with one another in a length direction and having a polygonal shape
in a cross-section perpendicular to the length direction, wherein
the large-capacity through holes are sealed at one end of the
porous ceramic members, the small-capacity through holes are sealed
at the other end of the porous ceramic members, and the
large-capacity through holes have a total cross-section area which
is larger than a total cross-section area of the small-capacity
through holes.
2. The honeycomb structural body according to claim 1, wherein the
porous ceramic members are combined with one another with a sealing
material therebetween.
3. The honeycomb structural body according to claim 1, wherein a
distance between centers of gravity in the cross-section of the
nearest large-capacity through holes is equal to a distance between
centers of gravity in the cross-section of the nearest
small-capacity through holes.
4. The honeycomb structural body according to claim 1, wherein the
large-capacity through holes and/or the small-capacity through
holes have a polygonal shape.
5. The honeycomb structural body according to claim 1, wherein the
large-capacity through holes and/or small-capacity through holes
have chamfered corner portions in the cross-section.
6. The honeycomb structural body according to claim 1, wherein the
small-capacity through holes have a quadrangle or square shape in
the cross-section.
7. The honeycomb structural body according to claim 1, wherein a
ratio of a total cross-section area of the large-capacity through
holes to a total cross-section area of the small-capacity through
holes is set in a range from 1.01 to 9.00.
8. An exhaust gas purifying apparatus for a vehicle, comprising: a
plurality of porous ceramic members combined with one another, the
porous ceramic members each having a plurality of large-capacity
through holes and a plurality of small-capacity through holes
extending in parallel with one another in a length direction and
having a polygonal shape in a cross-section perpendicular to the
length direction, wherein the large-capacity through holes are
sealed at one end of the porous ceramic members, the small-capacity
through holes are sealed at the other end of the porous ceramic
members, and the large-capacity through holes have a total
cross-section area which is larger than a total cross-section area
of the small-capacity through holes.
9. The exhaust gas purifying apparatus according to claim 8,
wherein the porous ceramic members are combined with one another
with a sealing material therebetween.
10. The exhaust gas purifying apparatus according to claim 8,
wherein a distance between centers of gravity in the cross-section
of the nearest large-capacity through holes is equal to a distance
between centers of gravity in the cross-section of the nearest
small-capacity through holes.
11. The exhaust gas purifying apparatus according to claim 8,
wherein the large-capacity through holes and/or the small-capacity
through holes have a polygonal shape.
12. The exhaust gas purifying apparatus according to claim 8,
wherein the large-capacity through holes and/or small-capacity
through holes have chamfered corner portions in the
cross-section.
13. The exhaust gas purifying apparatus according to claim 8,
wherein the small-capacity through holes have a quadrangle or
square shape in the cross-section.
14. The exhaust gas purifying apparatus according to claim 8,
wherein a ratio of a total cross-section area of the large-capacity
through holes to a total cross-section area of the small-capacity
through holes is set in a range from 1.01 to 9.00.
15. The exhaust gas purifying apparatus according to claim 9,
wherein the sealing material comprises at least one binder selected
from the group consisting of an inorganic binder and an organic
binder.
16. The exhaust gas purifying apparatus according to claim 8,
wherein the large-capacity and small-capacity through holes bodies
are alternately formed in each of the porous ceramic members.
17. The exhaust gas purifying apparatus according to claim 8,
wherein each of the porous ceramic members has a quadrangle or
square shape in the cross-section.
18. The honeycomb structural body according to claim 1, wherein the
large-capacity and small-capacity through holes are alternately
formed in each of the structural bodies.
19. The honeycomb structural body according to claim 2, wherein the
sealing material comprises at least one binder selected from the
group consisting of an inorganic binder and an organic binder.
20. The honeycomb structural body according to claim 1, wherein
each of the porous ceramic members has a quadrangle or square shape
in the cross-section.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application claims benefit of priority to Japanese Patent
application Nos. 2002-267819 filed on Sep. 13, 2002, and 2003-57631
filed on Mar. 4, 2003, the contents of which are incorporated by
reference herein.
TECHNICAL FIELD
The present invention relates to a honeycomb structural body used
as a filter or the like for removing particulates and the like
contained in exhaust gases discharged from an internal combustion
engine such as a diesel engine.
BACKGROUND ART
In recent years, particulates, contained in exhaust gases that are
discharged from internal combustion engines of vehicles such as
buses and trucks and construction equipment, have raised serious
problems since those particulates are harmful to the environment
and the human body.
For this reason, various honeycomb structural bodies, made from
porous ceramics, have been proposed as filters capable of
collecting particulates from exhaust gases to purify the exhaust
gases.
Conventionally, with respect to the above-mentioned honeycomb
structural body, a columnar honeycomb structural body 30 in which,
as shown in FIG. 6, a number of through holes 31 are placed in
parallel with one another in the length direction with partition
wall 33 interposed therebetween has been known. As shown in FIG.
6(b), the through hole 31 is sealed with a sealing material 32 at
either of ends of its exhaust gas inlet side or exhaust gas outlet
side, so that exhaust gases that have entered one through hole 31
are discharged from another through hole 31 after having always
passed through the partition wall 33 that separates the through
holes 31. In other words, when the honeycomb structural body 30 is
installed in an exhaust gas passage of an internal combustion
engine, particulates in exhaust gases discharged from the internal
combustion engine are captured by the partition wall 33 when
passing through the honeycomb structural body 30, so that the
exhaust gases are purified.
Moreover, with respect to such a honeycomb structural body, the
following structure has been proposed: a through hole with the end
on the exhaust gas outlet side being sealed (hereinafter, also
referred to as inlet-side through hole) is formed as a through hole
with a larger capacity (hereinafter, also referred to as
large-capacity through hole) and a through hole with the end on the
exhaust gas inlet side being sealed (hereinafter, also referred to
as outlet-side through hole) is formed as a through hole with a
smaller capacity (hereinafter, also referred to as small-capacity
through hole), so that the aperture ratio on the exhaust gas inlet
side is made relatively greater than the aperture ratio on the
exhaust gas outlet side.
JP Kokai Sho 56-124418 has disclosed a ceramic filter in which
through holes having shapes, such as a triangle, a hexagonal shape,
a circular shape and a swelled shape, are formed. Moreover, U.S.
Pat. No. 4,276,071 (FIGS. 5a and 5p), JP Kokai Sho 56-124417, JP
Kokai Sho 62-96717 and U.S. Pat. No. 4,364,761 (FIGS. 5a to 5p)
have disclosed arrangements similar to that of JP Kokai Sho
56-124418.
Microfilms of Japanese Utility Model Application No. 56-187890 (JU
Kokai Sho 58-92409 (FIG. 6, page 4) have disclosed an exhaust gas
filter in which triangular through holes and hexagonal through
holes are formed with cell pitches of large-capacity through holes
being set approximately in a range from 1.0 to 2.5 mm.
U.S. Pat. No. 4,416,676 (FIGS. 1 to 4) has disclosed a honeycomb
filter in which through holes having shapes, such as a triangle, a
square, an octagonal shape and a round shape, are formed while the
relationship between: the wall thickness between large-capacity
through holes; and the wall thickness between the large-capacity
through hole and the small-capacity through hole; being
defined.
JP Kokai Sho 58-196820, JP Kokoku Hei 3-49608 and U.S. Pat. No.
4,417,908 (FIGS. 3 to 17) have disclosed honeycomb filters in which
through holes having shapes such as a triangle, a square and a
hexagonal shape as well as honeycomb filters in which the number of
through holes on the inlet side is made greater than the number of
through holes on the outlet side so that the aperture rate on the
exhaust gas inlet side is made relatively greater than the aperture
rate on the exhaust gas outlet side.
U.S. Pat. No. 4,420,316 (FIGS. 6 to 9) has disclosed a honeycomb
filter in which the number of sealed through holes is modified,
which relates to a technique for improving the gas flow rate in the
wall portions.
JP Kokai Sho 58-150015 has disclosed a filter which is provided
with square through holes and rectangular through holes, with the
cross-sectional shape of the through holes being formed into a
tapered shape so as to be changed from the gas inlet side toward
the outlet side.
JP Kokai Hei 5-68828 and the Japanese Patent gazette No. 3130587
(page 1) have disclosed honeycomb filters in which triangular
through holes and hexagonal through holes are formed and the
capacity rate of the large-capacity through holes is set to 60 to
70% while the capacity rate of the small-capacity through holes is
set to 20 to 30%, with the cell pitch of the large-capacity through
holes being set to approximately in a range from 2.5 to 5.0 mm.
French Patent No. 2789327 has disclosed a filter that is provided
with through holes having shapes such as a rectangular shape, a
square shape, a hexagonal shape and an octagonal shape, with the
cross-sectional shape of the through holes being formed into a
tapered shape so as to be changed from the gas inlet side toward
the outlet side.
International Publication No. 02/100514 and JP Kokai 2001-334114
(FIG. 2) have disclosed filters in which through holes having a
round shape and a hexagonal shape are formed. These have also
disclosed filter elements in which the ratio of the total area of
the cross-section of small-capacity through holes to the total area
of the cross-section of large-capacity through holes is set in a
range from 40 to 120%.
International Publication No. 02/10562 has disclosed a filter in
which square through holes and hexagonal through holes are formed,
with the ratio of cross-sections thereof being set in a range from
3:1 to 4:1.
International Publication No. 03/20407 has disclosed a honeycomb
structural body in which square through holes are formed with a
varied ratio of cross-sectional areas.
In the honeycomb structural bodies described in these patent
documents, since the aperture ratio on the exhaust gas inlet side
is made relatively greater in comparison with the honeycomb
structural body in which the aperture ratio on the exhaust gas
inlet side and the aperture ratio on the exhaust gas outlet side
are equal to each other, it becomes possible to increase the
limiting collection amount of particulates, to lengthen the period
up to the recovery process and to miniaturize the structure, when
used as a filter for purifying exhaust gases.
However, it has been found that, although these honeycomb
structural bodies slightly reduce the rate of increase in pressure
loss upon collection of particulates in comparison with a honeycomb
structural body in which the aperture ratio on the exhaust gas
inlet side and the aperture ratio on the exhaust gas outlet side
are equal to each other, they already have high pressure loss even
in a state having collected no particulates before the start of
use, and consequently have high pressure loss over the entire
period of use.
Moreover, the flow rate of exhaust gases is affected not only by
the relationship between the displacement of an internal combustion
engine that discharges exhaust gases and honeycomb structural body,
but also by the operation condition of the internal combustion
engine. For example, in the case of automobiles, the flow rate of
exhaust gases discharged from the internal combustion engine
fluctuates every moment in response to the driving modes (such as,
flat-way driving, slope-way driving, high speed driving and low
speed driving), and when the flow rate of exhaust gases increases,
the back pressure caused by the honeycomb structural body becomes
higher, resulting in an abrupt rise in pressure loss. In such
cases, since a load is imposed on an engine, the riding comfort of
the automobile deteriorates, resulting in a problem of giving the
discomfort to the driver.
SUMMARY OF THE INVENTION
The present invention has been made so as to solve the
above-mentioned problems, and an object thereof is to provide a
honeycomb structural body capable of increasing the limiting
collection amount of particulates, reducing the pressure loss in
the use and reducing fluctuations in the pressure loss even when
the flow rate of exhaust gases from the internal combustion engine
fluctuates.
The honeycomb structural body according to the present invention is
a columnar honeycomb structure in which a number of through holes
that are placed in parallel with one another in the length
direction with partition wall interposed therebetween, wherein the
above-mentioned plurality of through holes comprises:
a group of large-capacity through holes, with one end thereof being
sealed so as to cause the total of areas of cross-section
perpendicular to the length direction to become relatively greater;
and
a group of small-capacity through holes, with the other end thereof
being sealed so as to cause the total of areas of the
above-mentioned cross-section to become relatively smaller,
the above-mentioned honeycomb structural body comprising a
plurality of columnar porous ceramic member.
Additionally, with respect to the combination between the
above-mentioned group of large-capacity through holes and group of
small-capacity through holes, the following combinations are
listed: (1) a case where, with respect to each of through holes
constituting the group of the large-capacity through holes and each
of through holes constituting the group of the small-capacity
through holes, the areas of cross sections perpendicular to the
length direction are the same, while the number of the through
holes constituting the group of large-capacity through holes is
greater; (2) a case where, with respect to each of through holes
constituting the group of the large-capacity through holes and each
of through holes constituting the group of the small-capacity
through holes, the areas of cross sections thereof are different
from each other, with the numbers of the respective through holes
being different from each other; and (3) a case where, with respect
to each of through holes constituting the group of the
large-capacity through holes and each of through holes constituting
the group of the small-capacity through holes, the area of the
cross section of the through holes constituting the group of
large-capacity through holes is greater, with the numbers of the
through holes of the two groups being the same.
Moreover, with respect to the through holes constituting the group
of the large-capacity through holes and/or the through holes
constituting the group of the small-capacity through holes, those
through holes may be formed by using the through holes of one type
having the same shape and the same area of cross sections
perpendicular to the length direction, or may be formed by using
the through holes of two or more types having different shapes and
different areas of cross sections perpendicular to the length
direction.
Furthermore, with respect to each of the through holes constituting
the large-capacity through holes and/or the small-capacity through
holes, the shape, the cross-sectional area perpendicular to the
length direction, and the like may be different depending on
portions from one end toward the other end, and, for example,
through holes having a taper shape or the like may be used.
In accordance with the honeycomb structural body of the present
invention, since the group of large-capacity through holes and the
group of small-capacity through holes are provided, the aperture
ratio on the exhaust gas inlet side is made relatively greater by
using the group of large-capacity through holes as the through
holes on the inlet side, so that it becomes possible to reduce the
rise width of the pressure loss at the time the particulates are
accumulated. Consequently, in comparison with a honeycomb
structural body in which the aperture ratio on the exhaust gas
inlet side and the aperture ratio on the exhaust gas outlet side
are equal to each other, it becomes possible to increase the
limiting collection amount of particulates to consequently lengthen
the period up to the recovery process, and to accumulate a greater
amount of ashes remaining after the particulates have been burned
to consequently lengthen the service life.
Moreover, since the honeycomb structural body of the present
invention includes a plurality of columnar porous ceramic members,
it becomes possible to greatly reduce the rise width of the
pressure loss at the time the particulates are accumulated, and to
suppress fluctuations in the pressure loss even at the time that
the flow rate of exhaust gases fluctuates in response to the
driving state of the internal combustion engine. Furthermore, the
structure having a plurality of columnar porous ceramic members
makes it possible to reduce a thermal stress that is generated in
the use so that the heat resistance is improved, and also to freely
adjust the size thereof by properly increasing or reducing the
number of the columnar porous ceramic members.
In the honeycomb structural body of the present invention, the
plurality of columnar porous ceramic members are desirably combined
with one another through a sealing material layer. In the honeycomb
structural body of the present invention, since the columnar porous
ceramic members are combined with one another through the sealing
material layers, it becomes possible to effectively reduce the rise
width of the pressure loss at the time the particulates are
accumulated, and to suppress fluctuations in the pressure loss even
at the time that the flow rate of exhaust gases fluctuates in
response to the driving state of the internal combustion
engine.
In the honeycomb structural body of the present invention, the
distance between centers of gravity of cross sections perpendicular
to the length direction of the adjacently located through holes
constituting the group of large-capacity through holes is desirably
set to the same as the distance between centers of gravity of
cross-sections perpendicular to the length direction of the
adjacently located through holes constituting the group of
small-capacity through holes. In the honeycomb structural body of
the present invention, since the distance between centers of
gravity of cross-sections perpendicular to the length direction of
the adjacently located through holes constituting the group of
large-capacity through holes is set to the same as the distance
between centers of gravity of cross-sections perpendicular to the
length direction of the adjacently located through holes
constituting the group of small-capacity through holes, heat is
evenly dispersed upon recovery to easily provide an even
temperature distribution; thus, it becomes possible to reduce the
occurrence of cracks due to thermal stress even after repetitive
uses for a long period, and consequently to improve the durability.
Moreover, it is possible to easily convert the flow of exhaust
gases entering the honeycomb structural body into a turbulent
flow.
In the honeycomb structural body of the present invention, the
shapes of cross-section perpendicular to the length direction of
the through holes constituting the group of large-capacity through
holes and/or the through holes constituting the group of
small-capacity through holes are desirably formed into a polygonal
shape. When the shape of cross-sections perpendicular to the length
direction of those through holes constituting the group of
large-capacity through holes and/or those through holes
constituting the group of small-capacity through holes is formed
into a polygonal shape in the honeycomb structural body of the
present invention, it becomes possible to easily reduce the area of
the partition wall in the cross section perpendicular to the length
direction, and consequently to easily increase the aperture ratio;
thus, it is possible to achieve a honeycomb structural body that is
superior in durability and has a long service life.
In the honeycomb structural body of the present invention, those
through holes constituting the group of large-capacity through
holes and/or those through holes constituting the group of
small-capacity through holes desirably have cross-sections
perpendicular to the length direction, each of which has a curved
shape in the vicinity of each of the corner portions. When those
through holes constituting the group of large-capacity through
holes and/or those through holes constituting the group of
small-capacity through holes have R-chamfered and/or C-chamfered
corner portions in their cross sections perpendicular to the length
direction, in the honeycomb structural body of the present
invention, it becomes possible to prevent concentration of stress
at each of the corners of the through holes, and consequently to
prevent the generation of cracks.
In the honeycomb structural body of the present invention, a
cross-section perpendicular to the length direction of each of the
through holes constituting the group of the small-capacity through
holes is desirably formed into a quadrangle or square shape. When
the cross section perpendicular to the length direction of each of
the through holes constituting the group of the small-capacity
through holes is formed into a quadrangle or square shape in the
honeycomb structural body of the present invention, it becomes
possible to easily reduce the area of the partition wall in the
cross section perpendicular to the length direction, and
consequently to easily increase the aperture ratio; thus, it is
possible to achieve a honeycomb structural body that is superior in
durability and has a long service life.
In the honeycomb structural body of the present invention, the area
ratio of the cross section perpendicular to the length direction of
the group of the large-capacity through holes to the
above-mentioned cross section of the group of the small-capacity
through holes (cross-sectional area of the group of large-capacity
through holes/cross-sectional area of the group of small-capacity
through holes) is desirably set in a range from 1.01 to 9.00. When
the area ratio of the cross section perpendicular to the length
direction of the group of the large-capacity through holes to the
above-mentioned cross section of the group of the small-capacity
through holes (cross-sectional area of the group of large-capacity
through holes/cross-sectional area of the group of small-capacity
through holes) is set in a range from 1.01 to 9.00 in the honeycomb
structural body of the present invention, the aperture ratio on the
exhaust gas inlet side is made relatively greater so that it
becomes possible to effectively reduce the rise width of the
pressure loss at the time the particulates are accumulated, and
consequently to prevent the pressure loss from becoming too high at
the initial stage of the use.
The honeycomb structural body of the present invention is desirably
used for an exhaust gas purifying apparatus for vehicles. The
application of the honeycomb structural body of the present
invention to an exhaust gas purifying apparatus for vehicles makes
it possible to lengthen the period up to the recovery process, to
lengthen the service life, to reduce fluctuations in the pressure
loss even when the flow rate of exhaust gases fluctuates in
response to the driving state of the combustion engine, to improve
heat resistance, and to freely adjust the size of the
structure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view that schematically shows one example
of a honeycomb structural body of the present invention.
FIG. 2(a) is a perspective view that schematically shows one
example of a columnar porous ceramic member that constitutes the
honeycomb structural body shown in FIG. 1, and FIG. 2(b) is a
cross-sectional view taken along line A-A of the columnar porous
ceramic member shown in FIG. 2(a).
FIGS. 3(a) to 3(d) and 3(f) are cross-sectional views that
schematically show examples of cross sections perpendicular to the
length direction of the columnar porous ceramic members
constituting the honeycomb structural body of the present
invention; FIG. 3(e) is a cross-sectional view that schematically
shows a cross section perpendicular to the length direction of a
columnar porous ceramic member that constitutes a conventional
honeycomb structural body; and FIGS. 3(g) and 3(h) are
cross-sectional views that schematically show one example of cross
sections perpendicular to the length direction of two adjacently
located columnar porous ceramic members that constitute the
honeycomb structural body of the present invention.
FIG. 4 is a side view that schematically shows a state where a
honeycomb filter of the present invention is manufactured.
FIG. 5 is a cross-sectional view that schematically shows an
example of an exhaust gas purifying apparatus in which the
honeycomb structural body of the present invention is used.
FIG. 6(a) is a perspective view that schematically shows one
example of a conventional honeycomb structural body; and FIG. 6(b)
is a cross-sectional view taken along line B-B in FIG. 6(a).
FIG. 7 is a perspective view that schematically shows one example
of a honeycomb structural body.
FIG. 8 is a perspective view that schematically shows another
example of a honeycomb structural body.
FIG. 9 is a graph which indicates the relationship between the
pressure loss and the temperature of inflow exhaust gas in
association with the operation time (collection amount of
particulates) in honeycomb structural bodies in accordance with
Example 1 and Comparative Example 1.
FIG. 10 is a conceptual diagram that shows main factors that cause
pressure losses in the honeycomb structural body.
FIGS. 11(a) to 11(f) are cross-sectional views that schematically
show examples of cross sections perpendicular to the length
direction of columnar porous ceramic members that constitute the
honeycomb structural body of the present invention.
FIG. 12 is a cross-sectional view that schematically shows one
example of cross section perpendicular to the length direction of a
columnar porous ceramic member that constitutes the honeycomb
structural body of the present invention.
EXPLANATION OF SYMBOLS
10, 30 honeycomb structural body 13, 14 sealing material layer 15
ceramic block 20, 40, 50, 70, 90 columnar porous ceramic member
21a, 41a, 51a, 71a, 91a large-capacity through hole 21b, 41b, 51b,
71b, 91b small-capacity through hole 22, 32 sealing member 23, 33,
43, 53, 73, 93 partition wall 31 through hole
DETAILED DISCLOSURE OF THE INVENTION
A honeycomb structural body of the present invention relates to a
columnar honeycomb structural body in which a number of through
holes are placed in parallel with one another in the length
direction with partition wall being interposed therebetween, and
the through holes are constituted by a group of large-capacity
through holes, with one end thereof being sealed so as to make the
total of areas of the cross-section perpendicular to the length
direction relatively greater, and a group of small-capacity through
holes, with the other end thereof being sealed so as to make the
total of areas of the cross-section relatively smaller, and the
above-mentioned honeycomb structural body includes a plurality of
columnar porous ceramic members.
FIG. 1 is a perspective view that schematically shows one example
of a honeycomb structural body of the present invention, and FIG.
2(a) is a perspective view that schematically shows one example of
a columnar porous ceramic member that constitutes the honeycomb
structural body shown in FIG. 1, and FIG. 2(b) is a cross-sectional
view taken along line A-A of the columnar porous ceramic member
shown in FIG. 2(a).
As shown in FIGS. 1 and 2, in the honeycomb structural body 10 of
the present invention, a plurality of columnar porous ceramic
members 20 are combined with one another through sealing material
layers 14 to form a ceramic block 15, and a sealing material layer
13 that prevents exhaust gas leak is formed on the circumference of
the ceramic block 15.
Additionally, the honeycomb structural body 10 of the present
invention shown in FIGS. 1 and 2 is provided with the sealing
material layers 13 and 14; however, the honeycomb structural body
of the present invention may have a structure in which columnar
porous ceramic members 20 are just physically combined with one
another physically without the sealing material layers.
In the columnar porous ceramic member 20, a number of through holes
21 are placed in parallel with one another in the length direction
thereof, with partition wall 23 being interposed therebetween. The
through holes 21 are constituted by two kinds of through holes
having the same number, that is, large-capacity through holes 21a
with one end thereof being sealed by a sealing member 22 on the
outlet side of the columnar porous ceramic member 20 and
small-capacity through holes 21b with one end thereof being sealed
by the sealing member 22 on the inlet side of the columnar porous
ceramic member 20. In other words, in the columnar porous ceramic
member 20, the respective large-capacity through holes 21a
constituting the group of large-capacity through holes and
small-capacity through holes 21b constituting the group of
small-capacity through holes constitute a structure wherein cross
sections perpendicular to the length direction of the
large-capacity through holes 21a constituting the group of
large-capacity through holes occupy a greater area, with the
numbers of the two kinds of through holes being set to the same.
Therefore, the group of large-capacity through holes 21a has a
relatively greater area of cross sections perpendicular to the
length direction in comparison with the group of small-capacity
through holes 21b. Exhaust gases entered the large-capacity through
holes 21a are allowed to flow out from the small-capacity through
holes 21b after always passing through the partition wall 23 that
separate the through holes 21; thus, the partition wall 23 is
allowed to function as a filter.
As described in the section of BACKGROUND ART, it has been found
that, in a conventional honeycomb structural body, when the
aperture ratio on the exhaust gas inlet side is increased, the
pressure loss becomes higher in the initial stage of particulate
collection.
FIG. 10 is a conceptual diagram that shows main factors that cause
a pressure loss in the honeycomb structural body.
As shown in FIG. 10, the main factors that cause a pressure loss in
the honeycomb structural body are: {circle around (1)} an aperture
ratio on the exhaust gas inlet side: .DELTA.Pa, {circle around (2)}
friction upon passage through through holes ({circle around (2)}-1
inlet-side through hole: .DELTA.Pb-1, {circle around (2)}-2
outlet-side through hole: .DELTA.Pb-2), {circle around (3)}
resistance upon passage through partition wall: .DELTA.Pc and the
like.
In the honeycomb structural body that is provided with the group of
large capacity through holes and the group of small capacity
through holes, between the inlet-side through holes and the
outlet-side through holes, the total cross-sectional areas
perpendicular to the length direction are made different from each
other, so that, in comparison with a honeycomb structural body in
which the capacities of all the through holes are substantially
equal, in a state prior to collection of particulates, since the
cross-sectional area of the inlet-side through holes becomes
greater, exhaust gases are allowed to easily enter the inlet-side
through holes; thus, a pressure loss derived from the aperture
ratio on the inlet side and friction exerted upon passage through
inlet-side through holes ({circle around (1)}: .DELTA.Pa+{circle
around (2)}-1: .DELTA.Pb-1) can be reduced. In contrast, since the
cross-sectional area of the outlet-side through holes becomes
smaller, friction exerted upon passage through outlet-side through
holes ({circle around (2)}-2: .DELTA.Pb-2) is increased. Moreover,
since the volume of partition wall through which exhaust gases are
allowed to directly pass toward the outlet-side through holes, that
is, the partition wall (filtration area) portion of which separates
the inlet-side through hole and the outlet-side through hole
becomes smaller, resistance ({circle around (3)}: .DELTA.Pc)
exerted upon passage through the partition wall is increased.
Consequently, when the aperture ratio on the exhaust gas inlet side
is increased, the pressure loss becomes higher in the initial stage
of particulate collection.
Therefore, also in the honeycomb structural body 10 of the present
invention, since the group of large-capacity through holes 21a into
which exhaust gases are allowed to flow has a relatively greater
capacity than the group of small-capacity through holes 21b through
which, after passing through the partition wall 23, the exhaust
gases are allowed to pass, the area of (filtration area) partition
wall through which the exhaust gases pass is made smaller in
comparison with the honeycomb structural body in which all the
through holes have the same capacity, with the result that upon
transmission of exhaust gases and the like, the pressure loss
becomes slightly higher in the initial stage of particulate
collection.
The present inventors have studied hard, and found that when the
aperture ratio on the exhaust gas inlet side is increased, the
collection state of particulates in the honeycomb structural body
tends to vary, and that this variation in the collection state
further causes a rise in the pressure loss in the honeycomb
structural body in response to the collection of particulates.
In other words, in the case of a honeycomb structural body in which
the aperture ratio on the exhaust gas inlet side is not
specifically made relatively higher, the particulates are normally
collected in a manner so as to form an almost even thickness over
the partition wall. This is presumably because, since the flow-in
rate and flow-out rate of exhaust gases are not different so much,
even when particulates are at first deposited unevenly, the
resistance in partition wall on which the collection of
particulates has not progressed becomes relatively lower, as the
collection thereof has progressed, so that exhaust gases are
allowed to easily enter the corresponding portion, with the result
that the particulates are consequently collected evenly on the
partition wall.
In contrast, in the case of a honeycomb structural body in which
the aperture ratio on the exhaust gas inlet side is made relatively
higher, the particulates tend to be deposited in a greater amount
at the portion close to the outlet side (in the vicinity of the
sealing section) of the inlet-side through holes, and also tend to
be deposited in a smaller amount at the portion close to the inlet
side thereof. This is because, since the capacity of the inlet-side
through holes and the capacity of the outlet-side through holes are
different from each other, the flow-in rate of exhaust gases
flowing into the honeycomb structural body and the flow-out rate of
exhaust gases flowing out the honeycomb structural body are greatly
different from each other, with the result that the exhaust gases,
entered the inlet-side through hole at the greater flow rate, are
caused to once reach the inside end (in the vicinity of the sealing
section) easily, and after having circulated inside the through
hole, are then allowed to flow into the outlet-side through hole
through a portion having smaller resistance in a concentrate
manner. The uneven collecting processes of this type are
accelerated as the collection is carried out for a long time, with
the result that the pressure loss becomes higher.
The honeycomb structural body 10 of the present invention makes it
possible to prevent the occurrence of uneven collecting processes
even when the collection state of particulates changes due to an
increased aperture ratio on the exhaust gas inlet side, and
consequently to solve the problem of high pressure loss; thus, even
when the aperture ratio on the exhaust gas inlet side is made
higher, it becomes possible to suppress a rise in the pressure loss
due to collecting processes of particulates.
In other words, the honeycomb structural body 10 of the present
invention includes a plurality of columnar porous ceramic members
20.
Since the honeycomb structural body 10 of the present invention is
constituted by a plurality of columnar porous ceramic members 20,
there are portions at which the columnar porous ceramic members 20
are made in contact with each other through a sealing material
layer 14 (through a partition wall 23, when no sealing material
layer is formed) so that the aperture ratio is slightly reduced in
comparison with a honeycomb structural body that is constituted by
a single columnar porous ceramic member. Conventionally, it has
been considered that when the aperture ratio decreases, the
pressure loss increases due to a reduction in the filtration area;
however, the present inventors have found that, in spite of the
reduction in the aperture ratio, such a divided structure makes it
possible to further reduce the rise width of the pressure loss at
the time the particulates are accumulated, and have devised the
present invention.
The following description will discuss the reason why the divided
structure of the honeycomb structural body makes it possible to
reduce the rise width of the pressure loss at the time the
particulates are accumulated.
In the case of a honeycomb structural body having an integrated
structure having a high aperture ratio on the exhaust gas inlet
side, the end face on the exhaust gas inlet side is constituted by
three kinds of members, that is, through holes constituting a group
of large-capacity through holes, sealing members that seal the
through holes constituting a group of small-capacity through holes
and a wall (basically formed by repeated partition wall having a
fixed thickness), and most of exhaust gases that are allowed to
flow toward the end face directly flow into the through holes
constituting the group of large-capacity through holes. For this
reason, presumably, the exhaust gases that are allowed to flow into
the honeycomb structural body reach the inside end of the through
holes constituting the group of large-capacity through holes,
without any variations in the flow arose at the above-mentioned end
face, to cause the above-mentioned uneven collection of
particulates.
In contrast, in the case of a honeycomb structural body having a
divided structure having a high aperture ratio on the exhaust gas
inlet side, the end face on the exhaust gas inlet side is
constituted by four kinds of members, that is, through holes
constituting a group of large-capacity through holes, sealing
members that seal the through holes constituting a group of
small-capacity through holes, thin wall (basically formed by a
partition wall 23 having a fixed thickness) and a thick wall
(formed by a partition wall 23 of one columnar porous ceramic
member 20 and a partition wall 23 of another columnar porous
ceramic member 20 that are adjacent to each other and made in
contact with each other), and part of exhaust gases that are
allowed to flow toward the end face directly collide with the
above-mentioned thick wall to generate flows that expand in surface
directions on the end face so that a turbulence is caused in the
flow that is directly introduced into the through holes that
constitute the group of large-capacity through holes. For this
reason, it is possible to reduce the flow rate of exhaust gases
upon entering the through holes constituting the group of
large-capacity through holes, and it becomes possible to reduce the
amount of the exhaust gases that are allowed to flow at a great
flow rate to reach the sealing portion located at the farthest
inside end of the through holes constituting the group of
large-capacity through holes. In other words, by reducing the flow
rate of the exhaust gases inside the inlet-side through holes of
the honeycomb structural body, particulates can be evenly collected
by the partition wall inside the through holes so that it becomes
possible to reduce the pressure loss.
Moreover, since the honeycomb structural body 10 of the present
invention includes a plurality of columnar porous ceramic members
20, it is possible to reduce fluctuations in the pressure loss even
when the flow rate of exhaust gases fluctuates in response to the
driving state of the internal combustion engine. This is because,
as the flow rate of exhaust gases that are allowed to flow into the
end face becomes higher, the exhaust gases are more easily allowed
to enter as parallel flows so that the effect for reducing the flow
rate of exhaust gases is exerted more efficiently, and in contrast,
in the case where the flow rate of exhaust gases that are allowed
to flow to the end face is low, since the flow of the exhaust gases
has a disturbance, the honeycomb structural body is inherently
unlikely to cause uneven collection, the effect for reducing the
flow rate of exhaust gases becomes smaller. In other words, even
when the flow rate of exhaust gases that are allowed to flow into
the honeycomb structural body fluctuates due to the driving state
of the internal combustion engine, the flow rate of exhaust gases
inside the honeycomb structural body is maintained in a
comparatively stable state. For example, in the case of
automobiles, although the driving mode changes every moment during
the operation so that the number of revolutions, load and the like
change every moment in the internal combustion engine, the
honeycomb structural body of the present invention exerts effects
more efficiently in accordance with an increase in the flow rate of
exhaust gases so that it becomes possible to reduce adverse effects
that are given to the driver and the vehicle due to changes in the
driving mode.
Moreover, since the honeycomb structural body 10 of the present
invention includes a plurality of columnar porous ceramic members
20, it is possible to reduce thermal stress generated in the use,
and consequently to improve the heat resistance, and it is also
possible to freely change the size by properly reducing or
increasing the number of the columnar porous ceramic members 20.
For example, even in the case where, in an attempt to increase the
aperture ratio, the honeycomb structural body substantially has a
low density to become insufficient in strength, the thermal stress
can be reduced by using smaller divided members.
Furthermore, in the honeycomb structural body 10 of the present
invention, since a plurality of columnar porous ceramic members 20
are combined with one another through sealing material layers 14,
it becomes possible to reduce the rise width of the pressure loss
at the time the particulates are accumulated more effectively, and
also to suppress fluctuations in the pressure loss even at the time
that the flow rate of exhaust gases fluctuates in response to the
driving state of the internal combustion engine. These effects are
obtained presumably because the formation of the sealing material
layer 14 further reduces the aperture ratio, and the thickness of
the partition wall 23 is considered to become thicker at a portion
in which the columnar porous ceramic members 20 are made in contact
with each other.
Here, the sealing material layer 14 is desirably allowed to have a
bonding function.
Moreover, the sealing material layer 14 desirably has an elastic
property that is different from the elastic property of the
columnar porous ceramic member 20. In the case where the sealing
material layer 14 and the columnar porous ceramic member 20 have
different elastic properties from each other, for example, upon
receipt of a pressure from exhaust gases in only one of the
columnar porous ceramic members 20, only the corresponding one of
the columnar porous ceramic members 20 is allowed to finely vibrate
even when all the columnar porous ceramic members 20 are integrated
by the sealing material layers 14. In this manner, since the
individual columnar porous ceramic members 20 are allowed to
vibrate independently, the individual columnar porous ceramic
members 20 make it possible to individually collect particulates
evenly. In contrast, in the case where the sealing material layers
14 and the columnar porous ceramic members 20 have completely the
same elastic property, even when the individual columnar porous
ceramic members 20 try to vibrate independently, the entire
honeycomb structural body tends to move in the same manner, and
since considerably large vibration energy is required to generate
such a vibration in the entire honeycomb structural body, the
vibration actually tends to be cancelled. Therefore, in order to
accelerate even particulate-collecting processes and to reduce the
pressure loss, the columnar porous ceramic members 20 and sealing
material layers 14 desirably have mutually different elastic
properties.
With respect to the size of the honeycomb structural body 10 of the
present invention, not particularly limited, it is properly
determined by taking the size of an exhaust gas passage of the
internal combustion engine to be used, and the like into
consideration. Moreover, with respect to the shape of the honeycomb
structural body of the present invention, not particularly limited
as long as it is a column shape, for example, a desired shape, such
as a cylinder shape, an elliptical column shape and a rectangular
column shape, may be used; and, in general, a cylinder shape as
shown in FIG. 1 is used.
With respect to the material for the columnar porous ceramic
members in the honeycomb structural body of the present invention,
examples thereof may include, but not limited to, nitride ceramics
such as aluminum nitride, silicon nitride, boron nitride, titanium
nitride and the like, carbide ceramics such as silicon carbide,
zirconium carbide, titanium carbide, tantalum carbide and tungsten
carbide, and oxide ceramics such as alumina, zirconia, cordierite,
mullite and the like. Moreover, the columnar porous ceramic member
may be made from two kinds or more materials, such as a composite
material of silicon and silicon carbide, and aluminum titanate. In
particular, silicon carbide, which is superior in heat resistance
and mechanical properties, and also has high thermal conductivity,
is desirably used.
Although not particularly limited, the porosity of the columnar
porous ceramic members is desirably set to about 20 to 80%. When
the porosity is less than 20%, the honeycomb structural body of the
present invention is more susceptible to clogging, while the
porosity exceeding 80% causes degradation in the strength of the
columnar porous ceramic members, with the result that it might be
easily broken.
Here, the above-mentioned porosity can be measured through known
methods such as a mercury press-in method, Archimedes's method and
a measuring method using a scanning electronic microscope
(SEM).
The average pore diameter of the columnar porous ceramic members is
desirably set in a range from 5 to 100 .mu.m. The average pore
diameter of less than 5 .mu.m tends to cause clogging of
particulates easily. In contrast, the average pore diameter
exceeding 100 .mu.m tends to cause particulates to pass through the
pores, with the result that the particulates cannot be collected,
making the structural body unable to function as a filter.
With respect to the particle size of ceramic particles to be used
upon manufacturing the columnar porous ceramic members, although
not particularly limited, however ceramic particles which are less
susceptible to shrinkage in the succeeding firing process are
desirably used. For example, those particles, prepared by combining
100 parts by weight of ceramic particles having an average particle
size from 0.3 to 50 .mu.m with 5 to 65 parts by weight of ceramic
particles having an average particle size from 0.1 to 1.0 .mu.m,
are desirably used. By mixing ceramic powders having the
above-mentioned respective particle sizes at the above-mentioned
blending rate, it is possible to provide a porous material.
The sealing member is desirably made from porous ceramics. In the
honeycomb structural body of the present invention, since the
above-mentioned columnar porous ceramic member is made from porous
ceramics, by forming the sealing member using the same porous
ceramics as the porous ceramic member, it becomes possible to
increase the bonding strength of the two members, and by adjusting
the porosity of the sealing material in the same manner as the
above-mentioned columnar porous ceramic member, it becomes possible
to make the coefficient of thermal expansion of the columnar porous
ceramic member consistent with the coefficient of thermal expansion
of the sealing member; and it becomes possible to prevent a gap
from appearing between the sealing member and the partition wall
due to a thermal stress exerted upon manufacturing and using, and
also to prevent cracks from occurring in the sealing member and the
portion of the partition wall that is made in contact with the
sealing member.
In the case where the above-mentioned sealing member is made from
porous ceramics, not particularly limited, for example, the same
material as the ceramic material forming the above-mentioned
columnar porous ceramic members may be used.
In the honeycomb structural body of the present invention, the
sealing material layers 13 and 14 are formed between the columnar
porous ceramic members 20 as well as on the circumference of the
ceramic block 15. The sealing material layer 14, formed between the
columnar porous ceramic members 20, is allowed to function as a
bonding agent used for combining the columnar porous ceramic
members 20 with each other, and the sealing material layer 13,
formed on the circumference of the ceramic block 15, is allowed to
function as a sealing member for preventing exhaust gas leak from
the circumference of the ceramic block 15, when the honeycomb
structural body 10 of the present invention is installed in an
exhaust gas passage of an internal combustion engine.
With respect to the material for the sealing material layer, not
particularly limited, examples thereof include an inorganic binder,
an organic binder and a material made from inorganic fibers and/or
inorganic particles and the like.
Here, as described above, in the honeycomb structural body of the
present invention, the sealing material layers are formed between
the columnar porous ceramic members as well as on the circumference
of the ceramic block; and these sealing material layers may be made
from the same material or may be made from different materials. In
the case where the sealing material layers are made from the same
material, the blending ratio of the material may be the same or
different.
With respect to the inorganic binder, for example, silica sol,
alumina sol and the like may be used. Each of these may be used
alone or two or more kinds of these may be used in combination.
Among the inorganic binders, silica sol is more desirably used.
With respect to the organic binder, examples thereof may include
polyvinyl alcohol, methyl cellulose, ethyl cellulose and
carboxymethyl cellulose. Each of these may be used alone or two or
more kinds of these may be used in combination. Among the organic
binders, carboxymethyl cellulose is more desirably used.
With respect to the inorganic fibers, examples thereof may include
ceramic fibers, such as silica-alumina, mullite, alumina, silica
and the like. Each of these may be used alone or two or more kinds
of these may be used in combination. Among the inorganic fibers,
silica-alumina fibers are more desirably used.
With respect to the inorganic particles, examples thereof include
carbides, nitrides and the like, and specific examples may include
inorganic powder or whiskers made from silicon carbide, silicon
nitride, boron nitride and the like. Each of these may be used
alone, or two or more kinds of these may be used in combination.
Among the inorganic fine particles, silicon carbide having superior
thermal conductivity is desirably used.
Here, the sealing material layer 14 may be made from a dense
material or may be made from a porous material so as to allow
exhaust gases to enter the inside thereof, and on the contrary, the
sealing material layer 13 is desirably made from a dense material.
This is because the sealing material layer 13 is formed so as to
prevent exhaust gas leak from the circumference of the ceramic
block 15 when the honeycomb structural body 10 of the present
invention is placed in an exhaust passage of an internal combustion
engine.
In the honeycomb structural body of the present invention having a
structure as shown in FIG. 1, the distance between centers of
gravity of cross-sections perpendicular to the length direction of
the adjacently located through holes constituting the group of
large-capacity through holes is desirably equal to the distance
between centers of gravity of cross-sections perpendicular to the
length direction of the adjacently located through holes
constituting the group of small-capacity through holes. With this
arrangement, heat is evenly dispersed upon recovery so that the
temperature distribution is easily made even; thus, it is possible
to provide a honeycomb structural body that is less likely to
generate cracks and the like due to thermal stress even after
long-term repeated uses, and has superior durability.
Moreover, in the case of such a honeycomb structural body having
the same distance between centers of gravity, for example, as shown
in the honeycomb structural body 70 of FIG. 3(d), a difference in
thickness of partition wall may be formed based upon a difference
in sizes of the through holes on the peripheral portion, or, for
example, as shown in the honeycomb structural body 90 of FIG. 3(f),
a flow of exhaust gases to enter the honeycomb structural body on
the peripheral portion is allowed to easily form a turbulent flow
by installing through holes 92 having an intermediate size on the
peripheral portion.
In addition, as shown in FIG. 3(g), by locating the large-capacity
through holes adjacent to each other through a sealing member, the
flow of exhaust gases to enter the honeycomb structural body is
caused to easily form a turbulent flow in the same manner.
Here, in the present specification, "the distance between centers
of gravity of cross-sections perpendicular to the length direction
of the adjacently located through holes constituting the group of
large-capacity through holes" refers to a minimum distance between
the center of gravity of a cross-section perpendicular to the
length direction of one through hole that constitutes the group of
large-capacity through holes and the center of gravity of a
cross-section perpendicular to the length direction of another
through hole that constitutes the group of large-capacity through
holes, and "the distance between centers of gravity of
cross-sections perpendicular to the length direction of the
adjacently located through holes constituting the group of
small-capacity through holes" refers to a minimum distance between
the center of gravity of a cross-section perpendicular to the
length direction of one through hole that constitutes the group of
small-capacity through holes and the center of gravity of a
cross-section perpendicular to the length direction of another
through hole that constitutes the group of small-capacity through
holes.
Moreover, in this honeycomb structural body, the through holes
constituting the group of large-capacity through holes and the
through holes constituting the group of small-capacity through
holes are alternately arranged in the longitudinal direction and/or
in the lateral direction with a partition wall being interposed
therebetween, and the center of gravity of a cross-section
perpendicular to the length direction of each of through holes that
constitute the group of large-capacity through holes and the center
of gravity of a cross-section perpendicular to the length direction
of each of through holes that constitute the group of
small-capacity through holes in each of the directions are located
on a straight line.
Therefore, "the distance between centers of gravity of
cross-sections perpendicular to the length direction of the
adjacently located through holes constituting a group of
large-capacity through holes" and "the distance between centers of
gravity of the cross-sections of the adjacently located through
holes constituting a group of small-capacity through holes" refer
to a distance between centers of gravity of each large-capacity
through hole 21a and each small-capacity through hole 21b that are
diagonally adjacent to each other in cross sections perpendicular
to the length direction of the honeycomb structural body 10 of the
present invention.
In the honeycomb structural body of the present invention, the
shapes of cross section perpendicular to the length direction of
each of through holes constituting the group of large-capacity
through holes and/or a cross section perpendicular to the length
direction of each of through holes constituting the group of
small-capacity through holes is desirably a polygonal shape. The
application of a polygonal shape makes it possible to reduce the
area of partition wall in the cross section perpendicular to the
length direction of the honeycomb structural body; thus, it becomes
possible to easily increase the aperture ratio, and consequently to
achieve a honeycomb structural body that has superior durability
and a long service life.
In the present invention, among polygonal shapes, those having four
or more apexes are desirably used, and in particular, the
cross-sectional shape of the large-capacity through hole is
desirably set to an octagonal shape. This is because, when a round
shape or an elliptical shape is used, the cross-sectional area of
the partition wall becomes greater, making it difficult to increase
the aperture ratio. Here, only the cross section of through holes
constituting the group of large-capacity through holes may be a
polygonal shape such as a quadrangle shape, a pentagonal shape, a
hexagonal shape, a trapezoidal shape and an octagonal shape, or
only the cross section of through holes constituting the group of
small-capacity through holes may be the above-mentioned polygonal
shape, or both of them may be a polygonal shape. Alternatively,
various polygonal shapes may be used in a mixed manner.
Additionally, the honeycomb structural body of the present
invention, the cross-sectional shape of the through holes is
desirably unchanged from the end face on the exhaust gas inlet side
to the end face on the exhaust gas outlet side. Thus, it becomes
possible to increase the compression strength, isostatic strength
and the like, and also to easily carry out manufacturing processes
through extrusion molding.
In the honeycomb structural body of the present invention, the area
ratio of the cross section perpendicular to the length direction of
the group of the large-capacity through holes to the
above-mentioned cross section of the group of the small-capacity
through holes (cross-sectional area of the group of large-capacity
through holes/cross-sectional area of the group of small-capacity
through holes; hereinafter, also referred to as aperture ratio) is
desirably set to have a lower limit value of 1.01 and an upper
limit value of 9.00. When the aperture ratio is less than 1.01, the
effects of installation of the group of large-capacity through
holes and the group of small-capacity through holes are hardly
obtained. In contrast, when the aperture ratio exceeds 9.00, the
capacity of the group of small-capacity through holes becomes too
small, with the result that the pressure loss tends to become too
large.
The lower limit value of the aperture ratio is desirably set to
1.3, more desirably, to 1.55, most desirably, to 2.0. The upper
limit value of the aperture ratio is desirably set to 2.75, more
desirably, to 2.54, most desirably, to 2.42. By setting the
aperture ratio to these values, it becomes possible to further
reduce the pressure loss at the time of collecting particulates
and, also, to increase the recovery limit value.
Here, the recovery limit value refers to a collected quantity (g/l)
of particulates that might cause cracks and the like in the
honeycomb structural body and subsequent damages to the honeycomb
structural body, upon carrying out the recovery process, if
particulates are collected beyond this value. Therefore, when the
recovery limit value is increased, it becomes possible to increase
the quantity of particulates that can be collected until the
recovery process is required, and consequently to lengthen the
period up to the recovery process.
FIGS. 3(a) to 3(d) and FIGS. 11(a) to 11(f) are cross-sectional
views each of which schematically shows one portion of a cross
section of each of columnar porous ceramic members that constitute
a honeycomb structural body of the present invention; and FIG. 3(e)
is a cross-sectional view that schematically shows one portion of a
cross section of a conventional honeycomb structural body.
The above-mentioned aperture ratio is set to about 1.55 in FIG.
3(a), it is set to about 2.54 in FIG. 3(b), it is set to about 4.45
in FIG. 3(c), it is set to about 6.00 in FIG. 3(d), and it is set
to about 1.00 in FIG. 3(e). In all the FIGS. 11(a), 11(c) and
11(e), the above-mentioned aperture ratio is set to about 4.45, and
in all the FIGS. 11(b), 11(d) and 11(f), the above-mentioned
aperture ratio is set to about 6.00. Here, in the columnar ceramic
member 70 shown in FIG. 3(d), the distance between centers of
gravity in cross sections of large-capacity through holes 71a
constituting a group of large-capacity through holes is equal to
the distance between centers of gravity in cross sections of
small-capacity through holes 71b constituting a group of
small-capacity through holes, and the aperture ratio thereof is
9.86, which is a very big value. As described above, in the case
where the aperture ratio is set to a great level exceeding 9.00,
the capacity of each of the small-capacity through holes 71b that
constitute a group of small-capacity through holes 71b into which
exhaust gases that have passed through the partition wall 73 are
allowed to flow is too small, with the result that the pressure
loss tends to become too large; therefore, in the present
invention, the porous ceramic members, shown in FIGS. 3(a) to 3(c),
are desirably used.
In the honeycomb structural bodies shown in FIGS. 3(a) to 3(d), the
large-capacity through holes and the small-capacity through holes
are arranged alternately; thus, the cross-sectional area of the
small-capacity through hole is changed, with the cross-sectional
shape of the large-capacity through hole being slightly changed, so
that the aperture ratio is easily varied desirably. In the same
manner, with respect to the honeycomb structural body shown in FIG.
11, the aperture ratio can be varied optionally.
In FIGS. 3(a) to 3(d), the cross-sectional shape perpendicular to
the length direction of each of the large-capacity through holes
that constitute a group of large-capacity through holes is set to
an octagonal shape, and the cross-sectional shape of each of the
small-capacity through holes that constitute a group of
large-capacity through holes is set to a quadrangle shape (square).
Here, the cross-sectional shape perpendicular to the length
direction of each of the small-capacity through holes that
constitute the group of small-capacity through holes is desirably
set to a quadrangle shape (square). This is because, it becomes
possible to easily achieve a honeycomb structural body of the
present invention having a structure as shown in FIGS. 3(a) to
3(d). Moreover, since the combination of an octagonal shape and a
quadrangle shape (square) provide a good symmetrical property,
exhaust gases are easily made to flow into the large-capacity
through hole evenly, and it is possible to improve the isostatic
strength and compression strength. Consequently, it becomes
possible to provide a honeycomb structural body having superior
resistance to the recovery process.
In honeycomb structural bodies 160 and 260 shown in FIGS. 11(a) and
11(b), the cross-sectional shapes of large-capacity through holes
161a and 261a that constitute the groups of large-capacity through
holes are set to a pentagonal shape, and in this shape, three
angles are set to substantially right angles, and the
cross-sectional shapes of small-capacity through holes 161b and
261b that constitute the groups of small-capacity through holes are
set to a quadrangle shape so that these are allowed to respectively
occupy portions of a larger quadrangle shape (square) that
diagonally face each other. In honeycomb structural bodies 170 and
270 shown in FIGS. 11(c) and 11(d) which have modified shapes of
the cross-sections shown in FIGS. 3(a) to 3(d), a partition wall
shared by each of large-capacity through holes 171a, 271a
constituting the group of large-capacity through holes and each of
small-capacity through holes 171b, 271b constituting the group of
small-capacity through holes is expanded toward the small-capacity
through hole side with a certain curvature. This curvature is
optionally set. In FIGS. 11(c) to 11(d), the curved line forming
the partition wall that is shared by each of large-capacity through
holes 171a, 271a and each of small-capacity through holes 171b,
271b may correspond to a 1/4 of the circle. In this case, the shape
that makes the aperture ratio smallest is approximately represented
by a shape shown in FIG. 11(c), and the aperture ratio at this time
is set to about 3.66.
In any of honeycomb structural bodies 180, 280 shown in FIGS. 11(e)
to 11(f), rectangular constituent units, each of which has a
large-capacity through hole 181a, 281a having a quadrangle shape
(rectangular shape) and a small-capacity through hole 281b, 281b
that are adjacent to each other longitudinally, are prepared, and
these constituent units are continuously placed in the longitudinal
direction, and also aligned in the lateral direction in a staggered
manner.
With respect to another specific example of the structures of the
through holes constituting the group of large-capacity through
holes and the group of small-capacity through holes in the
cross-sectional shape perpendicular to the length direction of the
honeycomb structural body of the present invention, for example, an
integrated honeycomb structural body 400 shown in FIG. 12, which
has large-capacity through holes 401 constituting the group of
large capacity through holes and small-capacity through holes 402
constituting the group of small capacity through holes, is
proposed.
The corner portions of a cross section perpendicular to the length
direction of each of the through holes constituting the group of
large-capacity through holes and/or each of the through holes
constituting the group of small-capacity through holes desirably
have chamfered faces, such as an R-chamfered face and/or a
C-chamfered face. Thus, it becomes possible to prevent
concentration of a stress at the corner portions of the through
hole, and consequently to prevent the occurrence of cracks.
In this specification, the R-chamfering refers to a chamfering
process which makes the corner circular arc. Moreover, the
C-chamfering refers to a chamfering process in which, by increasing
the number of sides forming the corner, neither acute angles nor
right angles are present on the corner.
Moreover, as shown in FIGS. 3(a) to 3(d), the corner portions on
the circumference of the columnar porous ceramic member desirably
have chamfered faces.
Next, the following description will discuss one example of a
manufacturing method for the honeycomb structural body of the
present invention.
First, a material paste mainly composed of ceramics as described
earlier is subjected to an extrusion-molding process so that a
ceramic formed body, which has a shape corresponding to the
above-mentioned columnar porous ceramic member 20 as shown in FIG.
2, is formed.
With respect to the above-mentioned material paste, although not
particularly limited, those pastes which allow the columnar porous
ceramic block 20 after the manufacturing processes to have a
porosity of 20 to 80% after the manufacturing processes, and, for
example, those pastes prepared by adding a binder and a dispersant
solution to the above-mentioned ceramic powder are desirably
used.
With respect to the above-mentioned binder, not particularly
limited, examples thereof include: methyl cellulose, carboxymethyl
cellulose, hydroxyethyl cellulose, polyethylene glycol, phenolic
resins, epoxy resins and the like.
Normally, the blend ratio of the above-mentioned binder is
desirably set to about 1 to 10 parts by weight to 100 parts by
weight of ceramic powder.
With respect to the above-mentioned dispersant solution, not
particularly limited, for example, an organic solvent such as
benzene, alcohol such as methanol, water and the like may be
used.
An appropriate amount of the above-mentioned dispersant solution is
blended so that the viscosity of the material paste is set in a
predetermined range.
These ceramic powder, binder and dispersant solution are mixed by
an attritor or the like, and sufficiently kneaded by a kneader or
the like, and then extrusion-molded so that the above-mentioned
ceramic formed body is formed.
Moreover, a molding auxiliary may be added to the above-mentioned
material paste, if necessary.
With respect to the molding auxiliary, not particularly limited,
examples thereof include: ethylene glycol, dextrin, fatty acid
soap, polyalcohol and the like.
Furthermore, a pore-forming agent, such as balloons that are fine
hollow spheres composed of oxide-based ceramics, spherical acrylic
particles and graphite, may be added to the above-mentioned
material paste, if necessary.
With respect to the above-mentioned balloons, not particularly
limited, for example, alumina balloons, glass micro-balloons,
shirasu balloons, fly ash balloons (FA balloons) and mullite
balloons may be used. In particular, fly ash balloons are more
desirably used.
Further, after the above-mentioned ceramic compact has been dried
by using a drier such as a microwave drier, a hot-air drier, a
dielectric drier, a reduced-pressure drier, a vacuum drier and a
frozen drier, predetermined through holes are filled with sealing
material paste to form sealing members so that a mouth-sealing
process for plugging the through holes is carried out.
With respect to the above-mentioned sealing material paste,
although not particularly limited, those pastes which allow the
resulting sealing members after the manufacturing process to have a
porosity of 20 to 80%, and, for example, the same material paste as
described above may be used; however, those pastes, prepared by
adding a lubricant, a solvent, a binder and a dispersant solution
to ceramic powder used as the above-mentioned material paste, are
desirably used. With this arrangement, it becomes possible to
prevent ceramics particles in the sealing material paste from
settling during the sealing process.
Next, the above-mentioned ceramic compact that has been subjected
to the drying process and the mouth-sealing process is subjected to
degreasing and sintering processes under predetermined conditions
so that the columnar ceramic member in which a plurality of through
holes are placed side by side in the length direction with a
partition wall interposed therebetween is manufactured.
Here, with respect to the degreasing and sintering conditions and
the like of the ceramic compact, it is possible to apply conditions
that have been conventionally used for manufacturing columnar
porous ceramic members.
Moreover, as shown in FIG. 4, columnar porous ceramic members 20
are placed on a base 80 the upper portion of which is designed to
have a V-shape in its cross-section so as to allow the columnar
ceramic members 20 to be stacked thereon in a tilted manner, and
sealing material paste to form a sealing material layer 14 is then
applied onto two side faces 20a and 20b facing upward with an even
thickness to form a sealing material paste layer 81; thereafter, a
laminating process for forming another columnar porous ceramic
member 20 on this sealing material paste layer 81 is successively
repeated so that a laminated body of rectangular columnar porous
ceramic members 20 having a predetermined size is manufactured.
With respect to the material for forming the above-mentioned
sealing material paste, since the description thereof has already
been given, the description thereof will not be given here.
Next, this laminated body of columnar porous ceramic members 20 is
heated so that the sealing material paste layer 81 is dried and
solidified to form a sealing material layer 14, and the
circumferential face of this is then cut into a shape as shown in
FIG. 1 by using a diamond cutter or the like; thus, a ceramic block
15 is manufactured.
Further, a sealing material layer 13 is formed on the circumference
of the ceramic block 15 by using the above-mentioned sealing
material paste so that the honeycomb structural body 10 of the
present invention, formed by combining a plurality of columnar
ceramic members 20 with one another through the sealing material
layers 14, is manufactured.
With respect to the application of the honeycomb structural body of
the present invention, although not particularly limited, it is
desirably used for exhaust gas purifying apparatuses for use in
vehicles.
FIG. 5 is a cross-sectional view that schematically shows one
example of an exhaust gas purifying apparatus for use in vehicles,
which is provided with the honeycomb structural body of the present
invention.
As shown in FIG. 5, an exhaust gas purifying apparatus 600 is
mainly constituted by a honeycomb structural body 60 of the present
invention, a casing 630 that covers the external portion of the
honeycomb structural body 60, a holding sealing material 620 that
is placed between the honeycomb structural body 60 and the casing
630 and a heating means 610 placed on the exhaust gas inlet side of
the honeycomb structural body 60, and an introducing pipe 640,
which is connected to an internal combustion device such as an
engine, is connected to one end of the casing 630 on the exhaust
gas inlet side, and a discharging pipe 650 externally coupled is
connected to the other end of the casing 630. In FIG. 5, arrows
show flows of exhaust gases.
In the exhaust gas purifying apparatus 600 having the
above-mentioned arrangement, exhaust gases, discharged from the
internal combustion device such as an engine, are directed into the
casing 630 through the introducing pipe 640, and allowed to flow
into the honeycomb structural body 60 through the inlet-side
through holes and to pass through the partition wall; thus, the
exhaust gases are purified, with particulates thereof being
collected in the partition wall, and are then discharged out of the
honeycomb structural body 60 through the outlet-side through holes,
and discharged outside through the exhaust pipe 650.
After a great quantity of particulates have been accumulated on the
partition wall of the honeycomb structural body 60 to cause an
increase in pressure losses, the honeycomb structural body 60 is
subjected to a recovering process.
In the recovering process, a gas, heated by using a heating means
610, is allowed to flow into the through holes of the honeycomb
structural body 60 so that the honeycomb structural body 60 is
heated to burn and eliminate the particulates deposited on the
partition wall.
Moreover, the particulates may be burned and eliminated by using a
post-injection system.
Moreover, the honeycomb structural body of the present invention
may have a catalyst capable of purifying CO, HC, NOx and the like
in the exhaust gases.
When such a catalyst is supported thereon, the honeycomb structural
body of the present invention is allowed to function as a filter
capable of collecting particulates in exhaust gases, and also to
function as a catalyst converter for purifying CO, HC, NOx and the
like contained in exhaust gases.
The above-mentioned catalyst may be supported on the porous surface
of the honeycomb structural body of the present invention, or may
be supported on the partition wall with a certain thickness.
Moreover, the above-mentioned catalyst may be evenly supported on
the porous surface and/or the surfaces, or may be supported on a
specific place in a biased manner. In particular, when the catalyst
is supported on the surfaces of the partition wall of the
inlet-side through holes or on the surfaces of pores in the
vicinity of the surface, or on both of the surfaces of these, the
catalyst is easily made in contact with the particulates so that
the particulates can be efficiently burned.
With respect to the catalyst to be supported on the honeycomb
structural body of the present invention, not particularly limited
as long as it can purify CO, HC, NOx and the like, examples thereof
include noble metals such as platinum, palladium and rhodium. The
catalyst, made from platinum, palladium and rhodium, is a so-called
three-way catalyst, and the honeycomb structural body of the
present invention which is provided with such a three-way catalyst
is allowed to function in the same manner as conventionally known
catalyst converters. Therefore, with respect to the case where the
honeycomb structural body of the present invention also functions
as a catalyst converter, detailed description thereof will not be
given.
BEST MODE FOR CARRYING OUT THE PRESENT INVENTION
The following description will discuss the present invention in
detail by means of examples; however, the present invention is not
intended to be limited by these examples.
EXAMPLE 1
(1) Powder of .alpha.-type silicon carbide having an average
particle size of 10 .mu.m (60% by weight) and powder of .beta.-type
silicon carbide having an average particle size of 0.5 .mu.m (40%
by weight) were wet-mixed, and to 100 parts by weight of the
resulting mixture were added and kneaded with 5 parts by weight of
an organic binder (methyl cellulose) and 10 parts by weight of
water to obtain a mixed composition. Next, after a slight amount of
a plasticizer and a lubricant have been added and kneaded therein,
the resulting mixture was extrusion-molded so that a formed
product, which had almost the same cross-sectional shape as the
cross-sectional shape shown in FIG. 3(a), was manufactured.
Next, the above-mentioned formed product was dried by using a
micro-wave drier to form a ceramic dried body, and predetermined
through holes were then filled with a paste having the same
composition as the formed product. After having been again dried by
using a drier, this was degreased at 400.degree. C., and sintered
at 2200.degree. C. in a normal-pressure argon atmosphere for 3
hours to manufacture a columnar porous ceramic member 20, which was
a silicon carbide sintered body, and had a porosity of 42%, an
average pore diameter of 9 .mu.m, a size of 36 mm.times.36
mm.times.150 mm, the number of through holes of 289 and a thickness
of the partition wall 23 of 0.4 mm, with the same number of
large-capacity through holes 21a and small-capacity through holes
21b being formed therein.
Here, on one end face of the columnar porous ceramic member 20,
only the large-capacity through holes 21a are sealed with a sealing
agent, and on the other end face thereof, only the small-capacity
through holes 21b are sealed with a sealing agent.
The width of a cross section perpendicular to the length direction
of the large-capacity through hole 21a was 1.65 mm, and the width
of the cross section of the small-capacity through hole 21b was
1.33 mm, and with respect to a cross section perpendicular to the
length direction of the columnar porous ceramic member 20, the
ratio of areas of the large-capacity through holes 21a was 38.2%,
and the ratio of areas of the small-capacity through holes 21b was
24.6%.
In the columnar porous ceramic member 20, the distance between
centers of gravity in cross sections of adjacently located
large-capacity through holes 21a and the distance between centers
of gravity in cross sections of adjacently located small-capacity
through holes 21b were 2.68 mm, and the aperture ratio was
1.55.
(2) By using a heat resistant sealing material paste containing 30%
by weight of alumina fibers having a fiber length of 0.2 mm, 21% by
weight of silicon carbide particles having an average particle size
of 0.6 .mu.m, 15% by weight of silica sol, 5.6% by weight of
carboxymethyl cellulose and 28.4% by weight of water, the processes
as described by reference to FIG. 4 were carried out so that, as
shown in FIG. 3(g), 16 (4.times.4) columnar porous ceramic members
20 were combined with one another, with the large-capacity through
holes being mutually made adjacent as well as with the
small-capacity through holes being mutually made adjacent, and this
was then cut by using a diamond cutter to form a cylindrical shaped
ceramic block having a size of 144 mm in diameter.times.150 mm in
length.
In this case, the thickness of the sealing material layers used for
combining the columnar porous ceramic members 20 was adjusted to
1.0 mm.
Next, ceramic fibers made from alumina silicate (shot content: 3%,
fiber length: 0.1 to 100 mm) (23.3% by weight), which served as
inorganic fibers, silicon carbide powder having an average particle
size of 0.3 .mu.m (30.2% by weight), which served as inorganic
particles, silica sol (SiO.sub.2 content in the sol: 30% by weight)
(7% by weight), which served as an inorganic binder, carboxymethyl
cellulose (0.5% by weight), which served as an organic binder, and
water (39% by weight) were mixed and kneaded to prepare a sealing
material paste.
Next, a sealing material paste layer having a thickness of 1.0 mm
was formed on the circumferential portion of the ceramic block by
using the above-mentioned sealing material paste. Further, this
sealing material paste layer was dried at 120.degree. C. so that a
cylinder-shaped honeycomb structural body was manufactured.
EXAMPLE 2
The same processes as Example 1 were carried out except that the
cross-sectional shape of the columnar porous ceramic member was
made almost the same as a cross-sectional shape shown in FIG. 3(b)
so that a honeycomb structural body was manufactured.
The thickness of the partition wall 43 of a columnar porous ceramic
member 40 in accordance with Example 2 was 0.4 mm, the width of a
cross section perpendicular to the length direction of the
large-capacity through hole 41a was 1.84 mm, and the width of the
cross section of the small-capacity through hole 41b was 1.14 mm,
and with respect to a cross section perpendicular to the length
direction of the columnar porous ceramic member 40, the ratio of
areas of the large-capacity through holes 41a was 46.0%, and the
ratio of areas of the small-capacity through holes 41b was
18.1%.
In the columnar porous ceramic member 40 of Example 2, the distance
between centers of gravity in cross sections of adjacently located
large-capacity through holes 41a and the distance between centers
of gravity in cross sections of adjacently located small-capacity
through holes 41b were 2.72 mm, and the aperture ratio was
2.54.
EXAMPLE 3
The same processes as Example 1 were carried out except that the
cross-sectional shape of the columnar porous ceramic member was
made almost the same as a cross-sectional shape shown in FIG. 3(c)
so that a honeycomb structural body was manufactured.
The thickness of the partition wall 53 of a columnar porous ceramic
member 50 in accordance with Example 3 was 0.4 mm, the width of a
cross section perpendicular to the length direction of the
large-capacity through hole 51a was 2.05 mm, and the width of the
cross section of the small-capacity through hole 51b was 0.93 mm,
and with respect to a cross section perpendicular to the length
direction of the columnar porous ceramic member 50, the ratio of
areas of the large-capacity through holes 51a was 53.5%, and the
ratio of areas of the small-capacity through holes 51b was
12.0%.
In the columnar porous ceramic member 50 of Example 3, the distance
between centers of gravity in cross sections of adjacently located
large-capacity through holes 51a and the distance between centers
of gravity in cross sections of adjacently located small-capacity
through holes 51b were 2.79 mm, and the aperture ratio was
4.45.
EXAMPLES 4 TO 6
A columnar porous ceramic member, which was made of a silicon
carbide sintered body having a porosity of 42%, an average pore
diameter of 9 .mu.m, a size of 72 mm.times.72 mm.times.150 mm, the
number of through holes of 1156 and a thickness of the partition
wall of 0.4 mm, with the same number of large-capacity through
holes 21a and small-capacity through holes 21b being formed
therein, was manufactured, and the same processes as those of
Examples 1 to 3 were carried out except that, as shown in FIG.
3(g), four (2.times.2) of these columnar porous ceramic members
were combined with one another, with the large-capacity through
holes being mutually made adjacent as well as with the
small-capacity through holes being mutually made adjacent, so that
a ceramic block was manufactured; thus, a cylinder-shaped honeycomb
structural body having a size of 144 mm in diameter.times.150 mm in
length was manufactured.
Here, in Example 4, the cross-sectional shape of the columnar
porous ceramic member was made almost the same as a cross-sectional
shape shown in FIG. 3(a); in Example 5, the cross-sectional shape
of the columnar porous ceramic member was made almost the same as a
cross-sectional shape shown in FIG. 3(b); and in Example 6, the
cross-sectional shape of the columnar porous ceramic member was
made substantially the same as a cross-sectional shape shown in
FIG. 3(c).
EXAMPLES 7 TO 9
A columnar porous ceramic member, which had almost the same
cross-sectional shape as that shown in FIG. 11(a), FIG. 11(c) or
FIG. 11(e), and was made of a silicon carbide sintered body having
a porosity of 42%, an average pore diameter of 9 .mu.m, a size of
36 mm.times.36 mm.times.150 mm and a thickness of the partition
wall of 0.4 mm, was manufactured, and the same processes as those
of Example 1 were carried out except that 16 (4.times.4) of these
columnar porous ceramic members were combined with one another so
that a ceramic block was manufactured; thus, a cylinder-shaped
honeycomb structural body having a size of 144 mm in
diameter.times.150 mm in length was manufactured.
Here, in Example 7, the cross-sectional shape of the columnar
porous ceramic member was made almost the same as a cross-sectional
shape shown in FIG. 11(a); in Example 8, the cross-sectional shape
of the columnar porous ceramic member was made almost the same as a
cross-sectional shape shown in FIG. 11(c); and in Example 9, the
cross-sectional shape of the columnar porous ceramic member was
made almost the same as a cross-sectional shape shown in FIG.
11(e).
With respect to a cross section perpendicular to the length
direction of the columnar porous ceramic member, the ratio of areas
of the large-capacity through holes was about 52% in any one of the
members, and the ratio of areas of the small-capacity through holes
was about 13% in any one of the members, with the aperture ratio
being set to 4.45. In the columnar porous ceramic members of
Examples 7 to 9, the distance between centers of gravity in cross
sections of adjacently located large-capacity through holes and the
distance between centers of gravity in cross sections of adjacently
located small-capacity through holes were set to the same
value.
EXAMPLES 10 TO 12
A columnar porous ceramic member, which was made of a silicon
carbide sintered body having a porosity of 42%, an average pore
diameter of 9 .mu.m, a size of 72 mm.times.72 mm.times.150 mm and a
thickness of the partition wall of 0.4 mm, was manufactured, and
the same processes as those of Examples 7 to 9 were carried out
except that four (2.times.2) of these columnar porous ceramic
members were combined with one another so that a ceramic block was
manufactured; thus, a cylinder-shaped honeycomb structural body
having a size of 144 mm in diameter.times.150 mm in length was
manufactured.
Here, in Example 10, the cross-sectional shape of the columnar
porous ceramic member was made substantially the same as a
cross-sectional shape shown in FIG. 11(a); in Example 11, the
cross-sectional shape of the columnar porous ceramic member was
made almost the same as a cross-sectional shape shown in FIG.
11(c); and in Example 12, the cross-sectional shape of the columnar
porous ceramic member was made almost the same as a cross-sectional
shape shown in FIG. 11(e).
EXAMPLE 13 TO 15
A columnar porous ceramic member, which had almost the same
cross-sectional shape as that shown in FIG. 7, FIG. 8 or FIG. 12,
and was made of a silicon carbide sintered body having a porosity
of 42%, an average pore diameter of 9 .mu.m, a size of 72
mm.times.72 mm.times.150 mm (square column shape) and a thickness
of the partition wall of 0.4 mm, was manufactured, and the same
processes as those of Example 1 were carried out except that four
(2.times.2) of these columnar porous ceramic members were combined
with one another so that a ceramic block was manufactured; thus, a
cylinder-shaped honeycomb structural body having a size of 144 mm
in diameter.times.150 mm in length was manufactured.
Here, FIG. 7 is a cross-sectional view that schematically shows a
cross section perpendicular to the length direction of a honeycomb
structural body 200, and this honeycomb structural body 200 has a
structure in which small-capacity through holes 202 having a
triangle shape in the cross section are placed on the circumference
of each large-capacity through hole 201 having a hexagonal shape in
the cross section.
FIG. 8 is a cross-sectional view that schematically shows a cross
section perpendicular to the length direction of a honeycomb
structural body 300, and this honeycomb structural body 300 has a
structure in which small-capacity through holes 302 having a
laterally elongated hexagonal shape in the cross section are placed
on the circumference of each large-capacity through hole 301 having
a positive hexagonal shape in the cross section. Further,
large-capacity through holes 301 having a positive hexagonal shape
and large-capacity through holes 303 having a trapezoidal shape are
placed side by side.
In Example 13, the cross-sectional shape of the columnar porous
ceramic member is made almost the same as the cross-sectional shape
shown in FIG. 7; in Example 14, the cross-sectional shape of the
columnar porous ceramic member is made almost the same as the
cross-sectional shape shown in FIG. 8; and in Example 15, the
cross-sectional shape of the columnar porous ceramic member is made
substantially the same as the cross-sectional shape shown in FIG.
12.
In the columnar porous ceramic members, the ratios of areas of the
large-capacity through holes in a cross section perpendicular to
the length direction were respectively set to about 48% (Example
13), about 34% (Example 14) and about 51% (Example 15), the ratios
of areas of the small-capacity through holes were respectively set
to about 16% (Example 13), about 26% (Example 14) and about 10%
(Example 15), and the aperture ratios were respectively set to 3
(Example 13), 1.28 (Example 14) and 5 (Example 15).
EXAMPLES 16 TO 18
The same processes as Examples 1 to 3 were carried out except that,
upon combining 16 (4.times.4) columnar porous ceramic members 20,
these members were combined so that the large-capacity through
holes were not made adjacent to each other and so that the
small-capacity through holes were not made adjacent to each other,
as shown in FIG. 3(h); thus, a honeycomb structural body was
manufactured.
Here, Example 16 corresponds to Example 1, Example 17 corresponds
to Example 2, and Example 18 corresponds to Example 3.
EXAMPLES 19 TO 21
The same processes as Examples 1 to 3 were carried out except that,
instead of combining 16 (4.times.4) columnar porous ceramic members
20 by using sealing material paste, a partition wall member having
a thickness of 1.0 mm, made of a silicon carbide sintered body, was
inserted between the columnar porous ceramic members 20 and that a
sealant paste layer was not formed on the peripheral portion; thus,
a cylinder-shaped honeycomb structural body having a size of 144 mm
in diameter.times.150 mm in length was manufactured.
Here, in the honeycomb structural bodies in accordance with
Examples 19 to 21, the columnar porous ceramic members 20 are not
bonded to one another; however, upon using as an exhaust gas
purifying apparatus or the like, these are physically tightened
together, and used as one integral part.
Further, Example 19 corresponds to Example 1, Example 20
corresponds to Example 2, and Example 21 corresponds to Example
3.
COMPARATIVE EXAMPLES 1 TO 3
A columnar porous ceramic member, which was made of a silicon
carbide sintered body having a porosity of 42%, an average pore
diameter of 9 .mu.m, a size of 144 mm.times.144 mm.times.150 mm,
the number of through holes of 4624 and a thickness of the
partition wall of 0.4 mm, with the same number of large-capacity
through holes 21a and small-capacity through holes 21b being formed
therein, was manufactured, and the same processes as those of
Examples 1 to 3 were carried out except that the peripheral portion
of each of these columnar porous ceramic members was processed so
that a ceramic block was manufactured; thus, a cylinder-shaped
honeycomb structural body having a size of 144 mm in
diameter.times.150 mm in length was manufactured.
Here, in Comparative Example 1, the cross-sectional shape of the
columnar porous ceramic member was made almost the same as a
cross-sectional shape shown in FIG. 3(a); in Comparative Example 2,
the cross-sectional shape of the columnar porous ceramic member was
made almost the same as a cross-sectional shape shown in FIG. 3(b);
and in Comparative Example 3, the cross-sectional shape of the
columnar porous ceramic member was made almost the same as a
cross-sectional shape shown in FIG. 3(c).
COMPARATIVE EXAMPLE 4
The same processes as Example 1 were carried out except that the
cross-sectional shape of the columnar porous ceramic member was
made almost the same as a cross-sectional shape shown in FIG. 3(e)
so that a honeycomb structural body was manufactured.
The thickness of the partition wall of a columnar porous ceramic
member in accordance with Comparative Example 4 was 0.4 mm, the
width of one side in a cross section perpendicular to the length
direction of the through hole was 1.49 mm, and with respect to a
cross section perpendicular to the length direction of the columnar
porous ceramic member, the ratio of areas of the through holes was
30.6%.
In other words, in the columnar porous ceramic member of
Comparative Example 4, the distance between centers of gravity in
cross-sections of the through holes was 2.67 mm, and the aperture
ratio was 1.00.
COMPARATIVE EXAMPLES 5 TO 7
A columnar porous ceramic member, which was made of a silicon
carbide sintered body having a porosity of 42%, an average pore
diameter of 9 .mu.m, a size of 144 mm.times.144 mm.times.150 mm and
a thickness of the partition wall of 0.4 mm, was manufactured, and
the same processes as those of Examples 7 to 9 were carried out
except that the circumferential portion of each of these columnar
porous ceramic members was processed so that a ceramic block was
manufactured; thus, a cylinder-shaped honeycomb structural body
having a size of 144 mm in diameter.times.150 mm in length was
manufactured.
Here, in Comparative Example 5, the cross-sectional shape of the
columnar porous ceramic member was made almost the same as a
cross-sectional shape shown in FIG. 11(a); in Comparative Example
6, the cross-sectional shape of the columnar porous ceramic member
was made almost the same as a cross-sectional shape shown in FIG.
11(c); and in Comparative Example 7, the cross-sectional shape of
the columnar porous ceramic member was made almost the same as a
cross-sectional shape shown in FIG. 11(e).
COMPARATIVE EXAMPLES 8 TO 10
A columnar porous ceramic member, which was made of a silicon
carbide sintered body having a porosity of 42%, an average pore
diameter of 9 .mu.m, a size of 144 mm.times.144 mm.times.150 mm
(rectangular column shape) and a thickness of the partition wall of
0.4 mm, was manufactured, and the same processes as those of
Examples 13 to 15 were carried out except that the circumferential
portion of each of these columnar porous ceramic members was
processed so that a ceramic block was manufactured; thus, a
cylinder-shaped honeycomb structural body having a size of 144 mm
in diameter.times.150 mm in length was manufactured.
Here, in Comparative Example 8, the cross-sectional shape of the
columnar porous ceramic member was made almost the same as a
cross-sectional shape shown in FIG. 7; in Comparative Example 9,
the cross-sectional shape of the columnar porous ceramic member was
made almost the same as a cross-sectional shape shown in FIG. 8;
and in Comparative Example 10, the cross-sectional shape of the
columnar porous ceramic member was made substantially the same as a
cross-sectional shape shown in FIG. 12.
(Evaluation Method)
(1) Collection State of Particulates
An exhaust gas purifying apparatus shown in FIG. 5 was manufactured
by installing each of the honeycomb structural bodies relating to
the respective examples and comparative examples in an exhaust
passage of an engine, and the engine was driven at the number of
revolutions of 2000 min.sup.- and a torque of 50 Nm for a
predetermined period of time so that the honeycomb structural body
was allowed to collect particulates of about 7 g/L. Then, the
honeycomb structural body was cut, and by observing the cross
section, the thickness of the collected particulates was measured.
The measured portions were set to portions respectively 50 mm and
130 mm apart from the end face of the exhaust gas inlet side, in
the vicinity of the center (portions apart from the center by two
cells) of a cross section perpendicular to the length direction.
The ratio (50 mm measured value/130 mm measured value) between the
measured value at the portion of 50 mm and the measured value at
the portion of 130 mm was found. The results are shown in Table
1.
(2) Collection Limit
An exhaust gas purifying apparatus shown in FIG. 5 was manufactured
by installing each of the honeycomb structural bodies relating to
the respective examples and comparative examples in an exhaust
passage of an engine, and the engine was driven at the number of
revolutions of 2000 min.sup.-1 and a torque of 50 Nm for a
predetermined period of time, and the recovering process was then
successively carried out while increasing the driving time so that
the honeycomb structural body was examined for occurrence of any
cracks. Here, the quantity of particulates that had been collected
at the time of occurrence of a crack was defined as a collection
limit value. The results are shown in Table 1.
(3) Variation in Pressure Loss
An exhaust gas purifying apparatus shown in FIG. 5 was manufactured
by installing each of the honeycomb structural bodies relating to
Example 1 and Comparative Example 1 in an exhaust passage of an
engine of 3L, and the engine was driven constantly at the number of
revolutions of 2000 min.sup.- while the flow rate of the exhaust
gas was changed by increasing the load (torque) from 10 Nm by 2.5
Nm for every 15 minutes in a separate manner in 10 stages; thus,
the relationship between the pressure loss (102 mmAq=1 KPa) and the
flow-in temperature of the exhaust gas with respect to the driving
time (quantity of collection of particulates). The results are
shown in FIG. 9.
TABLE-US-00001 TABLE 1 Thickness ratio of Collection limit
particulates (g/L) Example 1 0.92 8.6 Example 2 0.85 9.5 Example 3
0.82 8.7 Example 4 0.80 7.9 Example 5 0.72 8.8 Example 6 0.65 8.0
Example 7 0.84 8.5 Example 8 0.86 8.6 Example 9 0.86 8.6 Example 10
0.72 7.8 Example 11 0.74 7.9 Example 12 0.73 7.9 Example 13 0.68
7.1 Example 14 0.66 7.6 Example 15 0.64 7.0 Example 16 0.80 8.5
Example 17 0.80 9.3 Example 18 0.75 8.6 Example 19 0.75 8.3 Example
20 0.71 9.0 Example 21 0.68 8.0 Comparative 0.45 6.1 Example 1
Comparative 0.40 7.0 Example 2 Comparative 0.32 6.2 Example 3
Comparative 0.92 7.8 Example 4 Comparative 0.37 6.0 Example 5
Comparative 0.39 6.1 Example 6 Comparative 0.39 6.1 Example 7
Comparative 0.31 4.6 Example 8 Comparative 0.29 5.1 Example 9
Comparative 0.27 4.5 Example 10
As clearly indicated by the results shown in Table 1, with respect
to the quantity of collection of particulates in the collection
limit, the honeycomb structural bodies in accordance with the
examples can collect more particulates than the honeycomb
structural bodies in accordance with the comparative examples,
thereby making it possible to lengthen the period up to the
recovery process.
Moreover, it has been found that each of the honeycomb structural
bodies in accordance with the examples makes the rise width of the
pressure loss smaller in comparison with the honeycomb structural
bodies in accordance with the comparative examples.
Moreover, the results shown in FIG. 9 indicate that, upon
increasing the flow rate of exhaust gases by changing the load at
the same number of revolutions, although the initial pressure loss
becomes higher than that of the integrated structure (comparative
examples), the divided structure, prepared by the examples,
gradually suppresses the rise in the pressure loss, thereby making
it possible to avoid abrupt changes in the pressure loss.
INDUSTRIAL APPLICABILITY
The honeycomb structural body of the present invention is provided
with a group of large-capacity through holes and a group of
small-capacity through holes so that by using the group of
large-capacity through holes as inlet-side through holes, the
aperture ratio on the exhaust gas inlet side is made relatively
greater; thus, it becomes possible to reduce the rise width of
pressure loss upon accumulation of particulates. Consequently, in
comparison with the honeycomb structural body in which the aperture
ratio on the exhaust gas inlet side and the aperture ratio on the
exhaust gas outlet side are equal to each other, it becomes
possible to increase the limiting amount of particulate collection
to consequently lengthen the period up to the recovery process, and
to accumulate a greater amount of ashes remaining after the
particulates have been burned to consequently lengthen the service
life.
Moreover, the honeycomb structural body of the present invention is
constituted by a plurality of columnar porous ceramic members;
therefore, it becomes possible to effectively reduce the rise width
of the pressure loss at the time the particulates are accumulated,
and to suppress fluctuations in the pressure loss even at the time
that the flow rate of exhaust gases fluctuates in response to the
driving state of the internal combustion engine. Furthermore, it is
possible to reduce a thermal stress that is generated in the use so
that the heat resistance is improved, and to freely adjust the size
thereof by properly increasing or reducing the number of the
columnar porous ceramic members.
* * * * *